early direct sowing in April?

kawaiineko_gardener(5a)March 10, 2014

The thing about 'you can't sow because the ground is still frozen/muddy/wet' doesn't apply to me. They will be grown in containers.

They'll also be in an unheated greenhouse. I would only be doing cold hardy stuff (escarole, endive...both are bitter leafy green things), spinach, lettuce, an early variety of pak choi (baby Chinese cabbage) and beets (I read on the packet if it's 45 degrees or above, you can do early spring sowings).

Is this even possible? I can get row covers that protect against frost that will also provide additional heat. The other option would be using milk jugs to make miniature greenhouses for the seedlings.

Being in a greenhouse, will they get enough sun? It's not a clear, glass greenhouse, it has a white plastic covering.

What about watering? I think the soil will not be frozen because this will be done in containers, and the greenhouse will provide some boost in heat, thus increasing temperatures a little.

I don't want to waste seed and/or time if this really isn't feasible. Have never done early spring sowings, so need advice.

We have a clear plastic high tunnel type of unheated greenhouse. The ground never froze all winter (NH) inside. Spinach has continued to grow. I would be concerned about how hot your greenhouse gets during the day. Recently, on a sunny day, mine got up to 97 degrees F. Eliot Coleman has written at least two books on extending the growing season. He market gardens year round in Maine. We have an indoor/outdoor thermometer so I know how hot it gets in the high tunnel. The sides can roll up when it gets warmer. When it's warm all the time, the sides will stay up all the time and the door will stay open.

I try to get spinach planted in the open garden as soon as possible. One winter it wintered over and started growing again as soon as it started getting warm enough. Somewhere I read that spinach is day length sensitive and will bolt when the days get longer. I've had good crops ever since I started planting early.

Market gardens using high tunnels in our area are moving indoor grown (cold hardy plant) seedlings to their high tunnels right now. But, I wonder why you have white plastic instead of clear. You might not be getting enough light right now.

How cold will the coldest nights be? Keep in mind that a plastic greenhouse won't retain much heat at night (although it will to some extent if it has a concrete floor). A dry dirt floor is a poor heat source. A moist dirt floor is a good heat source but keeping it moist all the time is a good way to encourage diseases.

Not all cool weather crops are equally tolerant of cold. Spinach, carrots, broccoli, kale, collards and tatsoi are very hardy but lettuce, celery, beets, swiss chard, bok choy and endive are somewhat less hardy. A 20 degree frost, for example, will not harm the first group but could damage the second.

Row covers are a good idea. I'm sure it will work out for you but start off with the more cold-resistant crops first.

Don't forget to vent the greenhouse on hot days - spinach does not like germination temperatures over 70 degrees.